Purpose :
Visual fatigue is becoming a more prevalent health problem with the circulation of tablet-type computers and smart phones. However, objective measures to diagnose visual fatigue are not well established. Patients with intermittent exotropia occasionally complain of diplopia after work requiring prolonged eye strain, which suggests a break of binocular fusion occurs by visual fatigue due to near work. We developed a binocular wavefront sensor equipped with a liquid crystal shutter in which the intensity of the incoming light was linearly reduced and can evaluate the ability of binocular fusion maintenance (BFM). The present study aimed to investigate whether the ability of BFM could be a measure of visual fatigue after visual tasks.

Methods :
Forty healthy volunteers (38.2 ± 12.9 years; mean ±SD) participated in the study. The ability of BFM was assessed by measuring the transmittance of liquid crystals placed in front of the subjects’ non-dominant eye when binocular fusion was broken and vergence eye movement was induced. A questionnaire on subjective symptoms was given to the subjects before and after a visual task of 30 min.